Both of Bitcoin clients are connected with at least 8 connections, a few blocks have passed since. The transaction appeared as unconfirmed/offline? even though I sent it while I had like 33 connections.

It did not show up on the other client at all. What happened?

After restarting the bitcoin client now it just says unconfirmed

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That destination address does not show a pending (or confirmed) 450 BTC transaction. Either the generations/inputs were invalid or your client wasn't connected to the network (more likely, though still seems very odd). Start both clients with -rescan (to ensure neither has invalid data) and wait around as the 450 BTC sending wallet will occasionally retransmit the transaction.